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[clang] Report Diagnostic when builtin vector has negative size #166055

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Nov 3, 2025
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[clang] Report Diagnostic when builtin vector has negative size #166055

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[clang] Report Diagnostic when builtin vector has negative size
AmrDeveloper Nov 2, 2025
98f4923
Address code review comments
AmrDeveloper Nov 3, 2025
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3 changes: 3 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -390,6 +390,9 @@ Improvements to Clang's diagnostics
that were previously incorrectly accepted in case of other irrelevant
conditions are now consistently diagnosed, identical to C++ mode.

- Clang now emits a diagnostic in case `vector_size` or `ext_vector_type`
attributes are used with a negative size (#GH165463).

Improvements to Clang's time-trace
----------------------------------

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2 changes: 2 additions & 0 deletions clang/include/clang/Basic/DiagnosticSemaKinds.td
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Expand Up @@ -3510,6 +3510,8 @@ def err_init_method_bad_return_type : Error<
"init methods must return an object pointer type, not %0">;
def err_attribute_invalid_size : Error<
"vector size not an integral multiple of component size">;
def err_attribute_vec_negative_size
: Error<"vector must have non-negative size">;
def err_attribute_zero_size : Error<"zero %0 size">;
def err_attribute_size_too_large : Error<"%0 size too large">;
def err_typecheck_sve_rvv_ambiguous : Error<
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10 changes: 10 additions & 0 deletions clang/lib/Sema/SemaType.cpp
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Expand Up @@ -2358,6 +2358,11 @@ QualType Sema::BuildVectorType(QualType CurType, Expr *SizeExpr,
return QualType();
}

if (VecSize->isNegative()) {
Diag(SizeExpr->getExprLoc(), diag::err_attribute_vec_negative_size);
return QualType();
}

if (CurType->isDependentType())
return Context.getDependentVectorType(CurType, SizeExpr, AttrLoc,
VectorKind::Generic);
Expand Down Expand Up @@ -2427,6 +2432,11 @@ QualType Sema::BuildExtVectorType(QualType T, Expr *ArraySize,
return QualType();
}

if (vecSize->isNegative()) {
Diag(ArraySize->getExprLoc(), diag::err_attribute_vec_negative_size);
return QualType();
}

if (!vecSize->isIntN(32)) {
Diag(AttrLoc, diag::err_attribute_size_too_large)
<< ArraySize->getSourceRange() << "vector";
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13 changes: 13 additions & 0 deletions clang/test/SemaCXX/vector.cpp
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Expand Up @@ -786,3 +786,16 @@ const long long e = *0; // expected-error {{indirection requires pointer operand
double f = a - e; // expected-error {{cannot initialize a variable of type 'double' with an rvalue of type '__attribute__((__vector_size__(1 * sizeof(double)))) double' (vector of 1 'double' value)}}
int h = c - e; // expected-error {{cannot initialize a variable of type 'int' with an rvalue of type '__attribute__((__vector_size__(1 * sizeof(long)))) long' (vector of 1 'long' value)}}
}

typedef int v_neg_size __attribute__((vector_size(-8))); // expected-error{{vector must have non-negative size}}
typedef int v_neg_size_2 __attribute__((vector_size(-1 * 8))); // expected-error{{vector must have non-negative size}}
typedef int v_ext_neg_size __attribute__((ext_vector_type(-8))); // expected-error{{vector must have non-negative size}}
typedef int v_ext_neg_size2 __attribute__((ext_vector_type(-1 * 8))); // expected-error{{vector must have non-negative size}}
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@AaronBallman AaronBallman Nov 3, 2025

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Another test case to add which I think won't be handled currently but will after moving into the Build functions is: https://godbolt.org/z/avobhW3Yx

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@AmrDeveloper AmrDeveloper Nov 3, 2025

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Yes, it works. I just need to write this test in another file that allows C++11 extension to be able to use using

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@AmrDeveloper AmrDeveloper Nov 3, 2025

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I forgot i can use ifdef to make it for specific version :D

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@AmrDeveloper AmrDeveloper Nov 3, 2025 •
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I am not sure why the parameter name is ArraySize, not VectorSize or Size 🤔 ?

QualType Sema::BuildExtVectorType(QualType T, Expr *ArraySize, <---- SourceLocation AttrLoc)

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@AaronBallman AaronBallman Nov 3, 2025

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I think that's just a think-o through refactoring, probably. Would be fine to rename in an NFC commit, IMO.

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@AmrDeveloper AmrDeveloper Nov 3, 2025

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Thanks, I will create NFC for that soon @AaronBallman

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@AmrDeveloper AmrDeveloper Nov 3, 2025

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Done #166208



#if __cplusplus >= 201103L

template <int N> using templated_v_size = int __attribute__((vector_size(N))); // expected-error{{vector must have non-negative size}}
templated_v_size<-8> templated_v_neg_size; //expected-note{{in instantiation of template type alias 'templated_v_size' requested here}}

#endif